This invention relates to electrodes and has particular reference to electrodes for use in the electrolytic production of manganese dioxide.
The use of permanent titanium electrodes in electrometallurgy is increasing. The permanent titanium electrodes show advantages over the other materials in their durability and in their ability to produce good electrodeposits on a long-term basis. Unfortunately, however, titanium is an expensive metal and there are, therefore, substantial advantages to be obtained from using as small a quantity of titanium as is possible.
The introduction of the all-welded hanger bar units, as are, for example, described in British Pat. Nos. 1,415,793 and 1,460,089, has led to a general approval of these types of electrodes as suitable for use as cathodes in metal electrowinning and electrorefining. The overall durability of the electrodes is very good and the general appearance and resistance of the electrodes to damage is also good. For the reasons mentioned above, however, it is desirable to reduce the thickness of titanium to as thin a level as possible. The conventional thickness for titanium electrodes is of the order of 4 mm and there have been proposals to make sandwich-type constructions in which a core metal is coated with titanium on both sides and this core metal is, therefore, a means of reducing the cost of the electrode. Unfortunately, however it has proved to be very difficult to produce a commercial product by this method because the cost of forming the construction is high and the problems associated with cutting the electrodes or piercing the outer layer of material have so far proved insuperable.
Other methods of enhancing the rigidity of the electrodes used in electrolytic processes are to be found in British Pat. No. 951,766. This shows an electrode consisting essentially of a corrugated sheet of metal such as titanium, tantalum, niobium or zirconium and the corrugations may be in the form of rectagular waves or may even be re-entrant as are shown in FIGS. 1 and 2. Attempts have been made to produce corrugated sheets of material which are sufficiently strong as to be useful but sufficiently thin as to be economic. It has been found, however, that the reduction in thickness which can be afforded by corrugating the sheets is very small and the reduction in thickness hardly pays for the cost of corrugation. Overall, therefore, simple corrugated sheets have not proven to be economically viable in the thicknesses desired.
Anodes for use in the production of chlorine by the electrolytic diaphragm cell method are described in British Pat. No. 1,181,659. These anodes basically comprise a pair of rectangular titanium sheets which are formed into the shape of an open box and are spot welded along their edges. Tabs integral with the sheets are connected to a conductor bar. It is stated that the structure may be strengthened by ribbing of the parallel plates, but no details of such ribbing are given. It is not fully understood what is meant by the word ribbing.
There exist in the chlorine industry a number of examples of electrodes which are manufactured from two or more elements. These electrodes are normally connected by a central pole to a current feeder. An example of such a design is to be found in U.S. Pat. No. 3,795,603 or U.S. Pat. No. 3,746,631.
In U.S. Pat. No. 3,379,627 there is described an anode for the manufacture of oxygen-containing derivative of olefins and this anode is shown to be in the form of contiguous tubes connected at their lower end to a pair of current lead-in members. A similar design of anode is illustrated in FIG. 18 of U.S. Pat. No. 3,342,717, which states, in column 19, line 22, that the design may be fabricated by extrusion or machining.
A foraminate anode basket has also been proposed, see British Pat. No. 1,433,800, FIG. 3, in which corrugated foraminate members are welded to a hanger bar. Such anodes are not, however, intended for use in circumstances where a product is deposited electrolytically onto their surfaces.
It can be seen, therefore, that the prior art anodes of complex shape have not been proposed for uses in which a metal or metal oxide deposited onto the surface of the electrode in use. Where the electrodes have been used in circumstances such that a material is physically deposited on their surfaces the electrodes have heretofor been of simple planar shape.